Taking supplements of certain vitamins and minerals may help men with low fertility to become fathers, an international review by Auckland researchers has found.
The quality of New Zealand men's sperm has declined, reflecting an international trend whose causes are not certain but are said to include smoking and obesity and, more controversially, agricultural chemicals.
A fertility clinic study in Wellington and Auckland published in 2008 found the concentration of sperm in semen had more than halved in 20 years.
Nearly a third of couples' infertility is attributed to "male factors".
Now Auckland University researchers, analysing trials from around the world on the use of antioxidant supplements by men with "sub-fertility", have found that taking the capsules is associated with a more than four-fold increased rate of pregnancy and live birth. They also found "mostly positive effects" on sperm concentration and motility [movement].
"When trying to conceive as part of an assisted reproductive programme, it may be advisable to encourage men to take oral antioxidant supplements to improve their partners' chances of becoming pregnant," said Marian Showell, the lead author of the research paper, published on the Cochrane Database of Systematic Reviews.
"However, these conclusions are based on limited evidence.
"We need more head-to-head comparisons to understand whether any one antioxidant is performing better than any other."
Dr Guy Gudex, the medical director of fertility clinic Repromed Auckland, said he advised some partners of women undergoing fertility treatment to take a supplement whose original trial had found a doubling of the pregnancy rate.
The supplement contains vitamins C and E, zinc, folic acid, lycopene, garlic oil and selenium.
Dr Gudex recommended the supplement to men with an abnormal sperm count or a lifestyle factor, such as being a smoker or overweight, which might predispose them to increased sperm DNA damage, or if their partner was having recurrent miscarriages.
The DNA damage is thought to be caused by "oxidative stress", which results from oxygen-containing molecules that are chemically unstable. Antioxidants from certain foods and supplements can help to reduce the damage they cause.
Auckland University is undertaking a Cochrane review of female sub-fertility and antioxidant supplements.
Dr Gudex said, "We are increasingly recommending to women, particularly in cases of recurrent miscarriage, to consider taking an antioxidant. There's pretty good evidence for men for oxidative stress. There's no reason to think it wouldn't help women similarly and improve the genetic health of eggs."
* Analysed 34 trials.
* Involved 2876 couples undergoing IVF, sperm injections or other assisted reproductive techniques.
* Explored use of antioxidants, including vitamin E, L-carnitine, zinc and magnesium.
* More than four-fold increase in pregnancy and live birth rates.
* Mostly positive effects on sperm concentration and motility.